Tension indicating devices, in general, are well known and utilized in a variety of applications. The simplest form of such devices is designed merely to indicate when a predetermined tension has been reached as opposed to providing continuous tension readings. Such devices, for example, find use for attachment to cables in cranes so that a warning to a crane operator will be provided if a load to be lifted creates a tension in the cable greater than a predetermined or unsafe value.
Some of the known prior art tension indicating devices require feeding of an end of the cable through the device in order to attach the device to the cable. In large crane structures utilizing multiple cables, such a procedure for attachment can be time consuming and costly since the cable has to be disassembled from the crane. While tension devices are known which are designed to be attached to a cable without access to the ends of the cable, other problems arise, principally the problem of realizing consistent indications when the tension in the rope or cable changes from a low value, through a predetermined value to a high value and from a high value through a predetermined value to a low value. To provide consistency has resulted in fairly complicated indicating structures.
More particularly, prior art tension indicators of the type under consideration in the present invention utilize a frame having a three point contact with a portion of the rope or cable, the center point being laterally displaced to be out of alignment with the other two points so that when tension is applied in the rope or cable a component of the tension force acts at the center point tending to bring it into alignment with the other two points. Movement of this center point is restrained by a resilient means so that by measuring the physical deflection, an indication of tension is provided. The inconsistency in readings as described heretofore resides in the "hysteresis" characteristic of the resilient means opposing the deflection and, as mentioned, considerable structural sophistication has been provided to minimize this hysteresis. The overall result has been that while tension indicating devices are available, they are relatively expensive and complicated in construction and still leave much to be desired in providing consistent and accurate indications.